The popular wisdom is that nonprofits must be large to make a real difference and that significant social change is usually spearheaded by a rare, brilliant leader. But that thinking is misleading and counterproductive, says Geoff Mulgan, chief executive of NESTA, Britain’s National Endowment for Science, Technology and the Arts. More often than not, real change is created thanks to the cumulative efforts of many. Such collaboration has been vital to the success of Mr. Mulgan's program, Studio S